Commit message: conf: Fix segfault when parsing mdev types

Commit f1b0890 introduced a potential crash due to incorrect operator
precedence when accessing an element from a pointer to an array.

Backtrace below:

  #0  virNodeDeviceGetMdevTypesCaps (sysfspath=0x7fff801661e0 "/sys/devices/pci0000:00/0000:00:02.0", mdev_types=0x7fff801c9b40, nmdev_types=0x7fff801c9b48) at ../src/conf/node_device_conf.c:2676
  #1  0x00007ffff7caf53d in virNodeDeviceGetPCIDynamicCaps (sysfsPath=0x7fff801661e0 "/sys/devices/pci0000:00/0000:00:02.0", pci_dev=0x7fff801c9ac8) at ../src/conf/node_device_conf.c:2705
  #2  0x00007ffff7cae38f in virNodeDeviceUpdateCaps (def=0x7fff80168a10) at ../src/conf/node_device_conf.c:2342
  #3  0x00007ffff7cb11c0 in virNodeDeviceObjMatch (obj=0x7fff84002e50, flags=0) at ../src/conf/virnodedeviceobj.c:850
  #4  0x00007ffff7cb153d in virNodeDeviceObjListExportCallback (payload=0x7fff84002e50, name=0x7fff801cbc20 "pci_0000_00_02_0", opaque=0x7fffe2ffc6a0) at ../src/conf/virnodedeviceobj.c:909
  #5  0x00007ffff7b69146 in virHashForEach (table=0x7fff9814b700 = {...}, iter=0x7ffff7cb149e <virNodeDeviceObjListExportCallback>, opaque=0x7fffe2ffc6a0) at ../src/util/virhash.c:394
  #6  0x00007ffff7cb1694 in virNodeDeviceObjListExport (conn=0x7fff98013170, devs=0x7fff98154430, devices=0x7fffe2ffc798, filter=0x7ffff7cf47a1 <virConnectListAllNodeDevicesCheckACL>, flags=0)
          at ../src/conf/virnodedeviceobj.c:943
  #7  0x00007fffe00694b2 in nodeConnectListAllNodeDevices (conn=0x7fff98013170, devices=0x7fffe2ffc798, flags=0) at ../src/node_device/node_device_driver.c:228
  #8  0x00007ffff7e703aa in virConnectListAllNodeDevices (conn=0x7fff98013170, devices=0x7fffe2ffc798, flags=0) at ../src/libvirt-nodedev.c:130
  #9  0x000055555557f796 in remoteDispatchConnectListAllNodeDevices (server=0x555555627080, client=0x5555556bf050, msg=0x5555556c0000, rerr=0x7fffe2ffc8a0, args=0x7fffd4008470, ret=0x7fffd40084e0)
          at src/remote/remote_daemon_dispatch_stubs.h:1613
  #10 0x000055555557f6f9 in remoteDispatchConnectListAllNodeDevicesHelper (server=0x555555627080, client=0x5555556bf050, msg=0x5555556c0000, rerr=0x7fffe2ffc8a0, args=0x7fffd4008470, ret=0x7fffd40084e0)
          at src/remote/remote_daemon_dispatch_stubs.h:1591
  #11 0x00007ffff7ce9542 in virNetServerProgramDispatchCall (prog=0x555555690c10, server=0x555555627080, client=0x5555556bf050, msg=0x5555556c0000) at ../src/rpc/virnetserverprogram.c:428
  #12 0x00007ffff7ce90bd in virNetServerProgramDispatch (prog=0x555555690c10, server=0x555555627080, client=0x5555556bf050, msg=0x5555556c0000) at ../src/rpc/virnetserverprogram.c:302
  #13 0x00007ffff7cf042b in virNetServerProcessMsg (srv=0x555555627080, client=0x5555556bf050, prog=0x555555690c10, msg=0x5555556c0000) at ../src/rpc/virnetserver.c:137
  #14 0x00007ffff7cf04eb in virNetServerHandleJob (jobOpaque=0x5555556b66b0, opaque=0x555555627080) at ../src/rpc/virnetserver.c:154
  #15 0x00007ffff7bd912f in virThreadPoolWorker (opaque=0x55555562bc70) at ../src/util/virthreadpool.c:163
  #16 0x00007ffff7bd8645 in virThreadHelper (data=0x55555562bc90) at ../src/util/virthread.c:233
  #17 0x00007ffff6d90432 in start_thread () at /lib64/libpthread.so.0
  #18 0x00007ffff75c5913 in clone () at /lib64/libc.so.6

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>
CVE: CVE-2021-3559
CWE: CWE-119
Vulnerability description: A flaw was found in libvirt in the virConnectListAllNodeDevices API in versions before 7.0.0. It only affects hosts with a PCI device and driver that supports mediated devices (e.g., GRID driver). This flaw could be used by an unprivileged client with a read-only connection to crash the libvirt daemon by executing the 'nodedev-list' virsh command. The highest threat from this vulnerability is to system availability.

Project: libvirt
File: node_device_conf.c

virNodeDeviceGetMdevTypesCaps(const char *sysfspath,
                              virMediatedDeviceTypePtr **mdev_types,
                              size_t *nmdev_types)
{
    virMediatedDeviceTypePtr *types = NULL;
    size_t ntypes = 0;
    size_t i;

    /* this could be a refresh, so clear out the old data */
    for (i = 0; i < *nmdev_types; i++)
       virMediatedDeviceTypeFree(*mdev_types[i]);
    VIR_FREE(*mdev_types);
    *nmdev_types = 0;

    if (virMediatedDeviceGetMdevTypes(sysfspath, &types, &ntypes) < 0)
        return -1;

    *mdev_types = g_steal_pointer(&types);
    *nmdev_types = ntypes;

    return 0;
}